1. Introduction The Proposed Approach Case Study: Lake Binaba Simulation Process Results Conclusion
Short-term Evaporation Estimating from
Complex Small Lakes in (Semi-)Arid Regions
Ali Abbasi
Nick van de Giesen
Delft University of Technology
Water Resources Management
August 20, 2014
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2. Introduction The Proposed Approach Case Study: Lake Binaba Simulation Process Results Conclusion
Outline
1 Introduction
Evaporation
Estimating Evaporation
2 The Proposed Approach
Advantages
Approach Theory
Application of CFD
CFD Scenarios
Framework
3 Case Study: Lake Binaba
Description
4 Simulation Process
CFDEvapModel-ToolBox
5 Results
Results
6 Conclusion
Conclusion
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3. Introduction The Proposed Approach Case Study: Lake Binaba Simulation Process Results Conclusion
Evaporation
Evaporation
Why do we need to estimate Evaporation?
As a major component of the hydrologic cycle.
The largest one of water loss from lakes, especially in arid and
semi-arid regions.
Approximately one half of the stored water in shallow lakes may
be lost due to evaporation
Aects the storage eciency of small lakes,
Evaporation Food Security
Determining the evaporation precisely is critically important to
assessing the reliability of small reservoir in arid regions.
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4. Introduction The Proposed Approach Case Study: Lake Binaba Simulation Process Results Conclusion
Estimating Evaporation
Estimating Evaporation
Accurately estimate evaporation from water bodies:
The key element to make improvements in water storage
(reservoir) management
Estimating or measuring evaporation over a lake or reservoir is a
very dicult task
The required meteorological parameters rarely measured over the
water surface.
The thermal lag between the water body and land surfaces
renders
The land-based measurements inecient in parameterization of
open water evaporation
Evaporation: from Lake vs. from Land
Lake evaporation is largely uncoupled from the land
evapotranspiration
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5. Introduction The Proposed Approach Case Study: Lake Binaba Simulation Process Results Conclusion
Estimating Evaporation
Methods
A wide range of methods are available to estimate evaporation:
Measurements: evaporation pan,eddy correlation technique.
Mass balance(budget)method.
Energy budget methods.
Mass transfer method.
Combination methods.
Temperature and radiation base methods
CFD-based approach.
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6. Introduction The Proposed Approach Case Study: Lake Binaba Simulation Process Results Conclusion
Estimating Evaporation
Complexity
Estimating evaporation from water surface is ...!! :
Perhaps the most dicult component of all the hydrological cycle
components
Complex interactions between the components of the
lake-atmosphere system
Being a function of:
meteorological and climatological factors(temperature, relative
humidity, wind speed, etc.)
geology and physiography of water bodies(size, depth, shape,
advective, location, etc.)
Evaporation: a unique feature of each lake
Due to dependency of evaporation on these parameters, it is a unique
feature of each lake and developing a clearly an unique theoretical
method for its estimation could be inhibited
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7. Introduction The Proposed Approach Case Study: Lake Binaba Simulation Process Results Conclusion
Estimating Evaporation
Complexity
With respect to evaporation, lake and reservoirs quite dierent from
land surfaces:
The penetrating of suns energy into the water
Mixing the water column by surface motion
The large heat storage capacity of water
The density of water (approximately 1000 times dense more
dense than air)
Nearly constant evaporation rate for night and day
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8. Introduction The Proposed Approach Case Study: Lake Binaba Simulation Process Results Conclusion
Estimating Evaporation
Complexity
Evaporation from water surface
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9. Introduction The Proposed Approach Case Study: Lake Binaba Simulation Process Results Conclusion
Outline
1 Introduction
Evaporation
Estimating Evaporation
2 The Proposed Approach
Advantages
Approach Theory
Application of CFD
CFD Scenarios
Framework
3 Case Study: Lake Binaba
Description
4 Simulation Process
CFDEvapModel-ToolBox
5 Results
Results
6 Conclusion
Conclusion
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10. Introduction The Proposed Approach Case Study: Lake Binaba Simulation Process Results Conclusion
Advantages
Advantages
The propose approach is:
Based on mass-transfer(aerodynamic) method.
Moderate input data demands
A generalisable and cost eective approach
Using Computational Fluid Dynamics(CFD)as a very powerful
tool.
Assuming heat and mass transfer analogy
Drive convective heat transfer coecient and mass-transfer
coecients for a given water body
The spatial variation of the evaporation rate over the water
surface
Consider the advection eects under arid climate conditions
CFDEvapModel: CFD-based Evaporation Approach
Dierent Climate conditions, the Spatial Distribution of Evaporation
over the Water Surface and the eects of advection(oasis) over the
water surface
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11. Introduction The Proposed Approach Case Study: Lake Binaba Simulation Process Results Conclusion
Approach Theory
Approach Theory
Based on the mass-transfer(aerodynamic) method
E = f(u)(es ea)
f(u2) = a + bu2
Not all of the known processes are included in wind function.
Constants a and b are vary with climate, lake size, etc.
full-scale experiments can provide realistic wind function for
speci

12. c water bodies.
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13. Introduction The Proposed Approach Case Study: Lake Binaba Simulation Process Results Conclusion
Approach Theory
Approach Theory
The convective heat exchange between the air and the water surface:
Hs = hs(Tw Ta) =
Nu k
L
(Tw Ta)
The evaporation rate from a water surface:
Elake =
Sh D (Xs Xa)
L
Analogy between the mass and heat transport processes:
Nu
Prn =
Sh
Scn
) hm =
Sh:D
L
=
Nu:Scn:D
L:P rn =
hs:Scn:D
k:P rn
Mass transfer coecient(hm) is extracted from the heat transfer
coecient(hs) and consequently evaporation can be estimated from
water surface.
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14. Introduction The Proposed Approach Case Study: Lake Binaba Simulation Process Results Conclusion
Application of CFD
Application of CFD
Computational Fluid Dynamics(CFD) is used to:
Have a precise and applicable estimation of transfer coecients.
Simulating the air
ow and heat transfer over the water
surface(in ABL)
Dierent and complex con

15. guration of lake and its surroundings
can be analysed.
Very high spatial resolution data are obtained.
Dierent conditions of ABL can be considered(from stable to
unstable conditions).
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16. Introduction The Proposed Approach Case Study: Lake Binaba Simulation Process Results Conclusion
Application of CFD
Air Flow over the Water Surface
Continuity Equations
@uj
@xj
= 0; (1)
Momentum Equation
@ui
+
@t
@
@xj
(ujui)
@
@xj
eff
@ui
@xj
+
@uj
@xi
2
3
@uk
@xk
ij
=
@p
@xi
+ gi [1

17. (T Tref )]
Temperature Equation
@T
@t
+
@
@xj
(Tuj) eff
@
@xk
(
@T
@xk
) = 0
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18. Introduction The Proposed Approach Case Study: Lake Binaba Simulation Process Results Conclusion
Application of CFD
CFD Computational Domain
Computational domain with the boundaries
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19. Introduction The Proposed Approach Case Study: Lake Binaba Simulation Process Results Conclusion
Application of CFD
CFD Computational Domain
Generated computational Mesh for CFD simulation
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20. Introduction The Proposed Approach Case Study: Lake Binaba Simulation Process Results Conclusion
Application of CFD
Boundary Conditions
boundary conditions of the CFD model of ABL
Location boundary condition
Inlet boundary u = u
ln
z+z0
z0
v = 0 w = 0;
k = u2
p
C
r
C1 ln
z+z0
z0
+ C2;
= u3
(z+z0)
r
C1 ln
z+z0
z0
+ C2;
@
@z (T) = 0
Outlet boundary @
@x (u; v;w; k; ; T) = 0;
Lateral boundaries v = 0; @
@y (u;w; k; ; T) = 0;
Top boundary w = 0; @
@z (u; v; k; ; T) = 0;
Terrain boundary (u; v;w) = 0; @
@z (T) = 0 Standard(rough)Wallfunctions;
Lake boundary (u; v;w) = 0; @
@z (T) = 0; Standard(smooth)Wallfunctions;
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21. Introduction The Proposed Approach Case Study: Lake Binaba Simulation Process Results Conclusion
Application of CFD
Generating CFD Mesh
Generating a good computational grid is essential.
Concentration of grid points near the the lake boundary is more
clustered to cover the sharp gradients in resolved parameters
In this work, the mesh was generated with the SnappyHexMesh
utility available in OpenFOAM.
making balance between computational time and quality of the
simulated results.
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22. Introduction The Proposed Approach Case Study: Lake Binaba Simulation Process Results Conclusion
CFD Scenarios
De

23. ning Scenarios
De

24. ning scenarios regarding most important parameters:
Water surface temperature(Ts)
Air temperature(Ta)
Wind speed over the water surface(U2)
Atmospheric stability condition()
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25. Introduction The Proposed Approach Case Study: Lake Binaba Simulation Process Results Conclusion
CFD Scenarios
De

26. ning Scenarios
Dierent scenarios for CFD simulations
CFD Scenario Ta[C] Tw[C] RH[%] U2[m=s] [] stability condition
CFDEvap-01 37.7 32.073 25 0.50 11.963 stable
CFDEvap-02 37.7 32.073 25 1.50 0.8042 stable
CFDEvap-03 37.7 32.073 25 2.50 0.2522 stable
CFDEvap-04 37.7 32.073 25 5.00 0.0516 stable
CFDEvap-05 19.9 29.34 85 0.50 -34.916 unstable
CFDEvap-06 19.9 29.34 85 1.50 -4.156 unstable
CFDEvap-07 19.9 29.34 85 2.50 -1.482 unstable
CFDEvap-08 19.9 29.34 85 5.00 -0.317 unstable
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27. Introduction The Proposed Approach Case Study: Lake Binaba Simulation Process Results Conclusion
Framework
Framework
Lake Borders
(Points Cloud)
Dimensions
of the
CFD Domain
Preparing the CFD Computational Domain
Volume Mesh
Generation
(blockMesh
snappyHexMesh)
CFD Simulation
System
Regression for
Different Scenarios
(wind function)
Visualization
The Results
Producing
Graphs
Figures
To Analyse
Simulations
Results(CFD)
Pre-processing
Setting up the
Boundary
Conditions
Numerical Setup
And
Physical Parameters
Using T_a,T_w,RH
Calculating X_a,X_s
Heat and Mass Transfer Calculations
Surface Cleaning
and Reduction
(MehsLAb addMESh)
Surface
Reconstruction
(Generating STL)
Calculating
Convective Heat
Transfer
Coefficient(h_s)
Calculating
Convective
Mass Transfer
Coefficient(h_m)
Calculating
Distribution of
Evaporation
Over the water Surface
Calculating
Heat Flux(H_s) over
water Surface
Proposed CFD-based simulation to calculate evaporation from the water surface
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28. Introduction The Proposed Approach Case Study: Lake Binaba Simulation Process Results Conclusion
Outline
1 Introduction
Evaporation
Estimating Evaporation
2 The Proposed Approach
Advantages
Approach Theory
Application of CFD
CFD Scenarios
Framework
3 Case Study: Lake Binaba
Description
4 Simulation Process
CFDEvapModel-ToolBox
5 Results
Results
6 Conclusion
Conclusion
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29. Introduction The Proposed Approach Case Study: Lake Binaba Simulation Process Results Conclusion
Description
Description
Lake Binaba:
Location: an arti

30. cial lake located in northern Ghana
Surface: the average area of the lake surface is 4.5 km2
Average depth: only 3 m
Maximum depth: 7 m
Usage: a small reservoir, used as a form of infrastructure for the
provision of water
Air temperature:
uctuates between 24 C and 35 C
Water surface temperature: varies from 28 C to 33 C
Climate: (semi-)arid region
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31. Introduction The Proposed Approach Case Study: Lake Binaba Simulation Process Results Conclusion
Description
Location
Lake Binaba:
Figure: Location of lake Binaba
r
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32. Introduction The Proposed Approach Case Study: Lake Binaba Simulation Process Results Conclusion
Description
Location
Lake Binaba:
Figure: Location of lake Binaba(Google earth)
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33. Introduction The Proposed Approach Case Study: Lake Binaba Simulation Process Results Conclusion
Outline
1 Introduction
Evaporation
Estimating Evaporation
2 The Proposed Approach
Advantages
Approach Theory
Application of CFD
CFD Scenarios
Framework
3 Case Study: Lake Binaba
Description
4 Simulation Process
CFDEvapModel-ToolBox
5 Results
Results
6 Conclusion
Conclusion
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34. Introduction The Proposed Approach Case Study: Lake Binaba Simulation Process Results Conclusion
CFDEvapModel-ToolBox
Tools
using powerful, open-source and free of charge tools:
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35. Introduction The Proposed Approach Case Study: Lake Binaba Simulation Process Results Conclusion
CFDEvapModel-ToolBox
OpenFOAM
OpenFOAM: Open Source Field Operation and
Manipulation
Open-Source Library
Free of Charge
Running in LINUX OS
C++ Library
Linking with PYTHON
New solvers and BCs can be implemented by the user
Running in parallel on distributed processors
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36. Introduction The Proposed Approach Case Study: Lake Binaba Simulation Process Results Conclusion
Outline
1 Introduction
Evaporation
Estimating Evaporation
2 The Proposed Approach
Advantages
Approach Theory
Application of CFD
CFD Scenarios
Framework
3 Case Study: Lake Binaba
Description
4 Simulation Process
CFDEvapModel-ToolBox
5 Results
Results
6 Conclusion
Conclusion
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37. Introduction The Proposed Approach Case Study: Lake Binaba Simulation Process Results Conclusion
Results
Results
Distribution of sensible and latent heat
uxes over the water surface
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38. Introduction The Proposed Approach Case Study: Lake Binaba Simulation Process Results Conclusion
Results
Results
Relationship between wind speed and transfer coecients:
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39. Introduction The Proposed Approach Case Study: Lake Binaba Simulation Process Results Conclusion
Results
Results
Estimated sensible and latent heat
uxes using proposed approach:
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40. Introduction The Proposed Approach Case Study: Lake Binaba Simulation Process Results Conclusion
Results
Results
Estimated sensible and latent heat
uxes using proposed approach:
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41. Introduction The Proposed Approach Case Study: Lake Binaba Simulation Process Results Conclusion
Outline
1 Introduction
Evaporation
Estimating Evaporation
2 The Proposed Approach
Advantages
Approach Theory
Application of CFD
CFD Scenarios
Framework
3 Case Study: Lake Binaba
Description
4 Simulation Process
CFDEvapModel-ToolBox
5 Results
Results
6 Conclusion
Conclusion
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42. Introduction The Proposed Approach Case Study: Lake Binaba Simulation Process Results Conclusion
Conclusion
Conclusion
CFD is a powerful tool in analysing and designing water
resources issues.
The proposed methodology represents an useful framework in
estimating evaporation for water bodies.
the eects of advection and atmospheric instability are
considered.
the spatial distributions of sensible and latent heat
uxes over
the water surface can be estimated.
using the proposed approach is easily applicable and cost
eective in estimating evaporation from the water surface.
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43. Introduction The Proposed Approach Case Study: Lake Binaba Simulation Process Results Conclusion
Conclusion
Thanks
Thanks for your attention
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44. Introduction The Proposed Approach Case Study: Lake Binaba Simulation Process Results Conclusion
Conclusion
Questions?
More details: a.abbasi@tudelft.nl
11th International Conference on Hydroinformatics(HIC 2014)
August 2014
New York City, USA
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